Histamine complexes

The optical spectra of nitrophorins in the absence of added ligands show Soret band maxima at 403-404 nm. On binding NO, the Soret band shifts to 419-420 nm in NPl and NP4, and 421-423 nm in NP2 and NP3 (46, 48-50). Example spectra are shown in Fig. 5a. The direction of the Soret band shift identifies the oxidation state of the heme iron as being Fe(III) (51, 52). The a and (3 bands of the NO complexes are located near 570 and 535 nm, respectively. The histamine complexes have Soret maxima at 410-412 nm and broad a, (3 maxima between 580... 

Fig. 5. UV-visible spectra of recombinant Rhodnius NP4 (pH 8.0) (a) without ligand (solid line) and NO complex (dashed line) (b) without ligand (solid line) and histamine complex (dashed line). Reproduced with permission from Ret (48).

At the time that the first investigation of the histamine complex of native NPl was reported 26), no EPR signal was observed, and it was concluded that the reason for this lack of an EPR signal from an expected low-spin d heme center was that the signal was that of a fast-relaxing large gmax species whose EPR spectrum was too weak to be observed. However, when recombinant protein became available and... 

Using the spectral data of Fig. 22, and similar data obtained for the nitrophorins in the absence of NO and in the presence of histamine, imidazole, or 4-iodopyrazole, Nernst plots such as that shown in the insert of Fig. 22 were constructed, and the midpoint potentials of the nitrophorins and their NO and histamine complexes were calculated. The results are summarized in Table IV, where they are compared to those obtained earlier for NPl (49, 50, 55). All potentials are expressed vs NHE (+205 mV with respect to the Ag/AgCl electrode used in the spectroelectrochemical titrations and the Nernst plot shown in the insert of Fig. 22). It can be seen that the reduction potentials of all four nitrophorins in the absence of NO or histamine are within 20-40 mV of each other. The reduction potentials of their NO complexes, however, differ significantly from each other. For example, the reduction potential of NP4-NO is about 350 mV more positive than that of NP4 in the absence of NO, as compared to a 430 mV shift for NPl upon binding NO, and the positive shifts for NP2—NO and NP3—NO are somewhat smaller (318 and 336 mV, respectively, at pH 7.5) 49, 50). These differences relate to the ratios of the dissociation constants for the two oxidation states, as discussed later. 

In comparing histamine to imidazole as ligands to the nitrophorins, at pH 7.5 (the approximate pH of the tissues of the victim), the histamine complex is 1200 times more stable for NPl and NP4, and about... 

Fig. 23. The dissociation constants and redox stability of the NO and histamine complexes of the nitrophorins from the saliva of Rhodnius prolixus, and how they aid the insect in obtaining a sufficient blood meal. Modified from Ref (.31).

Thickness of the barrier layer, optimized at 220 nm [133], played a crucial role with respect to the chemosensor sensitivity, selectivity and LOD. So, eventually, the chemosensor architecture comprised a gold-film electrode, sputtered onto a 10-MHz resonator, coated with the poly(bithiophene) barrier layer, which was then overlaid with the MIP film. This architecture enabled selective determination of the amine at the nanomole concentration level. LOD for histamine was 5 nM and the determined stability constant of the MIP-histamine complex, XMn> = 57.0 M 1 [131], compared well with the values obtained with other methods [53, 136, 137]. Moreover, due to the adopted architecture, the dopamine chemosensor could determine this amine with the stability constant for the MIP-dopamine complex, XMip = (44.6 4.0) x 106 M-1 and LOD of 5 nM [133], which is as low as that reached by electroanalytical techniques [138]. The MIP-QCM chemosensor for adenine [132] also featured low, namely 5 nM, LOD and the stability constant determined for the MIP-adenine complex, XMIP = (18 2.4) x 104 M, was as high as that of the MIP-adenine complex prepared by thermo-induced co-polymer-ization [139]. The linear concentration range for determination of these amines extended to at least 100 mM. 

Cu(II)(histamine)Cl2 at l/50th the dose of histamine produced the same subliminal anaphylactic symptoms as histamine. Injection of CUSO4 2 min before the injection of a non-lethal dose of histamine caused death by anaphylactic shock in all mice within 10 min. The anaphylactic LD50 value for Cu(IIXhistamine)Cl2 was found to be 1/I6th the anaphylactic LDso dose of histamine. These data support the suggestion that histamine-induced vascular permeability as an acute phase inflammatory reaction may be mediated by a Cu-histamine complex following degranulation of mast cells in the connective tissue spaces. 

We suspect that we are extracting the cells which contain a heparin-histamine complex and probably a polypeptide-histamine complex. The gastrin we are studying may be histamine or a compound which has the color reactions of histamine. ... 

The complexes Ni(PIpip), where H2PIpip = pyridylbis[N(4)-(piperidyl)] thiosemi-carbazones, show vNiN at 461 cm and vNiS at 335 cm Metal-isotope and deuteriation experiments were used to assign skeletal modes for the nickel-histamine complexes Ni(hm)Cl2 (vNiNH2 401 cm ) and [Ni(hm)3] + (380... 

Table 16 Forward and backward rate constants for Cvf -serinate-ethylene-diamine-histamine complexes...

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